Time Dependent Sphere-to-Rod Growth of the Pluronic Micelles: Investigating the Role of Core and Corona Solvation in Determining the Micellar Growth Rate

Abstract

The salt induced sphere-to-rod growth in the micelles of the PEO-PPO triblock copolymers, Pluronic P123 (EO(20)PO(70)PEO(20)) and Pluronic P103 (EO(16)PO(61)PEO(16)), has been studied by dynamic light scattering (DLS), viscometry, and small angle neutron scattering (SANS) techniques. The observed micellar growths are found to be time dependent and have a strong variation in their growth rate with changing anion type and copolymer composition. The rate of growth increases rather significantly with an increase in the water structure making abilities of the anions along the Hofmeister series in the order Cl(-) < F(-)< (PO(4))(3-). This has been attributed to an increasing ability of these ions to dehydrate the micellar corona, a factor that plays an important role in inducing sphere-to-rod shape transition of the micelles. The copolymer composition also has a significant influence on the micellar growth rate, as the P103 with a smaller molecular weight than P123 shows a significantly faster growth of its micelles under similar conditions. The observed time dependence in micellar growth in these systems has been attributed to a slow micellar restructuring process necessary to attain the equilibrium structure of the micelles. A remarkable improvement in the growth rate of the micelles, however, could be achieved in the presence of ethanol, a solvent that has affinity toward both the PPO and PEO blocks. Our spectroscopic studies suggest that the observed improvement in the micellar growth rate by ethanol is due to an accelerated restructuring process of the micelles in the presence of the solvated micellar core. These studies thus highlight the role of changing core and corona solvation characteristics of the pluronic micelles in determining their rearrangement and the growth rate, which is first of its kind in the aqueous pluronic system.

pH induced tuning of size, charge and viscoelastic behavior of aqueous micellar solution of Pluronic ® P104–anthranilic acid mixtures: A scattering, rheology and NMR study

“…and different lyotropic liquid crystalline phases can be formed by these amphiphiles depending upon EO/PO ratio (which alters the hydrophilic lipophilic balance), solution conditions such as concentration, temperature, pressure and pH, presence of salts, solvent type and polarity. The presence of various additives such as electrolytes [10,11], non-electrolytes [12,13], hydrotropes [14], surfactants [15,16], ionic liquids [17] other water soluble polymers [7,18] can alter the self-assembling characteristics such as surface activity [19], and micellar characteristics [20][21][22]. There are also reports of tuning aggregate characteristics of Pluronics ® using end group functionalized block copolymers [9,23].…”

“…By modulating the phase behavior [24] of Pluronics ® using other additives, properties can be tuned to performance based applications. A plethora of modern techniques based on spectral [12], thermal [15,25] and scattering [15,21,22] methods have been employed to investigate aqueous solution behavior of Pluronics ® .…”

Protein delivery using mesoporous ceramic/polymer hybrid

“…where the PPO core size determines the aggregation number of micelles [136,137]. The outcome was coherent to the work reported by Yan and co-workers [49] where the BET surface area of mesoporous bioactive glasses (70S25C) synthesized by F127 and P123 was of 20 m 2 /g difference as well.…”

“…A similar dehydration was observed for the highly hydrophilic PEO chains at T > 60 °C [65,159]. As a result, the solubility and the volume of the PEO blocks were reduced, forcing the micelles to undergo restructuring to increase their aggregation number and PPO core radius [136,137], leading to an increase in pore size. However, the high molecular weight F127…”

Enhanced Efficacy of Pluronic Copolymer Micelle Encapsulated SCR7 against Cancer Cell Proliferation

“…One representative of such materials is Pluronic block copolymers that are amphiphilic synthetic polymers containing hydrophilic poly(ethylene oxide) (PEO) blocks and hydrophobic poly(propylene oxide) (PPO) blocks arranged in triblock structure: PEO‐PPO‐PEO . One of the advantages of working with block copolymers is the versatility in precisely controlling nanostructure . Because of their lower critical solution temperature (LCST), which is around body temperature they have been widely used in the development of controlled drug delivery systems based on sol‐gel phase conversion at the body temperature.…”